The invention relates to methods of producing compositions for the modulation of T cell function in the treatment of for example, autoimmune diseases, allergic responses, transplant rejection, and other immunological disorders. In particular, it concerns production of major histocompatibility complex (MHC) class I and class II proteins in prokaryotes that have been transformed with nucleotide sequences that code for the proteins. The MHC proteins are useful for making complexes that target T cells. The complexes comprise the MHC proteins and peptides representing fragments of antigens associated with the particular diseases. These complexes can be further conjugated to radioisotopes or other labels for diagnostic purposes, or to toxins or other substances which render the complexes therapeutically useful.
A number of pathological responses involving unwanted T cell activation are known. For instance, a number of allergic diseases have been associated with particular MHC alleles or are suspected of having an autoimmune component.
Other deleterious T cell-mediated responses include the destruction of foreign cells that are purposely introduced into the body as grafts or transplants from allogeneic hosts. This process, known as "allograft rejection," involves the interaction of host T cells with foreign MHC molecules. Quite often, a broad range of MHC alleles are involved in the response of the host to an allograft.
Autoimmune disease is a particularly important class of deleterious immune response. In autoimmune diseases, self-tolerance is lost and the immune system attacks "self" tissue as if it were a foreign target. More than 30 autoimmune diseases are presently known; these include many which have received much public attention, including myasthenia gravis (MG) and multiple sclerosis (MS).
The involvement of the MHC Class II proteins in autoimmune disease has been shown in animal models. Administration of antibodies to either MHC Class II proteins themselves or antibodies to agents that induce expression of the MHC Class II genes interferes with development of the autoimmune condition in these model systems. The role of helper T cells has also been demonstrated in these models by counteracting the autoimmune system using anti-CD4 monoclonal antibodies: CD4 is the characteristic helper T cell receptor (Shizuru, J. A. et al., Science (1988) 240: 659-662).
Recent experiments have shown that, under certain circumstances, anergy or nonresponsiveness can be induced in autoreactive lymphocytes (see, Schwartz, Cell (1989) 1073-1081). In vitro experiments suggest that antigen presentation by MHC Class II molecules in the absence of a co-stimulatory signal induces a state of proliferative non-responsiveness in syngeneic T cells (Quill et al., J. Immunol. (1987) 138: 3704-3712). As described by Sharma et al. (Proc. Natl. Acad. Sci. USA (1991) 88: 11465-11469) anergy can be induced in vivo and autoimmune disease can be effectively treated in this manner.
MHC polypeptides thus have several pharmaceutical uses. However, to realize the potential of these types of treatments, a source of abundant MHC polypeptides is needed. MHC polypeptides have been expressed in mammalian cells. For example, a soluble form of the mouse I-E.sup.k protein has been expressed in CHO cells (Wettsttein et. al., J. Exp. Med. 174: 219-228 (1991)). The expression levels from mammalian systems, however, are not sufficient for economical production of MHC polypeptides on a commercial scale. Moreover, mammalian cells load the MHC peptide binding pocket with endogenous peptides, necessitating peptide removal from the MHC. Thus, the prior art lacks methods for producing large quantities of therapeutically active MHC polypeptides at low cost. The present invention addresses these and other needs.